As coastal societies lived their lives they also left their mark. Sometimes through totems and carvings but almost always through discarded shells and scraps of bone from their food. These refuse heaps contain a wealth of information about how that community lived, what they ate and what environmental conditions looked like over time. This physical history provides a wonderful resource for archaeologists in search of botanical material, artifacts, broken cooking implements and my personal favourite, mollusc shells.
These wonderfully informative heaps of the local gastronomic record provide a wealth of information. Especially those formed from enormous mounds of bivalves and clams. We call these middens. Left over time, these unwanted dinner scraps transform through a process of preservation.
The Danish term køkkenmøddinger (plural) was first used by Japetus Steenstrup, a Danish zoologist and biologist, to describe shell heaps and continues to be used by some researchers. I still prefer middens, but to each his own. Time and pressure leach the calcium carbonate, CaCO3, from the surrounding marine shells and help “embalm” bone and antler artifacts that would otherwise decay. Useful this, as antler makes for a fine sewing tool when worked into a needle. Much of what we know around the modification of natural objects into tools comes from this preservation.
Calcium carbonate is a chemical compound that shares the typical properties of other carbonates. In prepping fossil specimens embedded in limestone, it is useful to know that limestone, itself a carbonate sedimentary rock, reacts with stronger acids, releasing carbon dioxide: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l).
Calcium carbonate reacts with water saturated with carbon dioxide to form the soluble calcium bicarbonate. Bone already contains calcium carbonate, as well as calcium phosphate, Ca2, but it is also made of protein, cells and living tissue.
Decaying bone acts as a sort of natural sponge that wicks in the calcium carbonate displaced from the shells. As protein decays inside the bone, it is replaced by the incoming calcium carbonate, making the bone harder and more durable.
The shells, beautiful in their own right, make the surrounding soil more alkaline, helping to preserve the bone and turning the dinner scraps into exquisite scientific specimens for future generations.